Did you know that we only dream of what we know?
Our dreams are frequently full of strangers who play out certain parts. Our mind is not inventing those faces, they are real faces of real people that you have seen during your life.
We have all seen hundreds of thousands of faces through our lives, so we have an endless supply of characters for our brain to utilize during our dreams.
This is also an explanation why you cannot experience dying in your dreams. If you’re, for example, dreaming that you are falling from the sky, the moment you hit the floor your mind will shift to something else.